OPA628 Burr-Brown, OPA628 Datasheet - Page 12

• Manufacturer Part Number: OPA628
• Description: Low Distortion Wideband OPERATIONAL AMPLIFIER
• Manufacturer: Burr-Brown

the amplifier’s input bias currents. Whenever possible, match
the impedance seen by both inputs as is shown with R
will reduce error due to the amplifier’s input bias current.
FIGURE 9. Offset Voltage Trim.
SPICE MODELS
Computer simulation using SPICE is often useful when
analyzing the performance of analog circuits and systems.
This is particularly true for Video and RF amplifier circuits
where parasitic capacitance and inductance can have a
major effect on circuit performance. SPICE models are
available for the OPA628. Contact Burr-Brown Applica-
tions Department to receive a SPICE diskette.
RELIABILITY DATA
Reliability reports are available upon request for each of the
package options offered.
PRINTED CIRCUIT BOARD GUIDELINES
The printed circuit board layout is critical to obtaining the
full performance of the OPA628, particularly optimum
distortion and gain flatness. The guidelines below should be
employed to design the OPA628 printed circuit board.
1. Establish the primary ground plane on the IC side of the
NOTE: (1) R
bias currents.
PC board. The primary ground plane is the lowest imped-
ance ground plane, it should be as wide as possible with
minimal interruptions. Connect all unused space on both
sides of the board to the ground plane. The ground plane
should extend beneath the body of the IC on both sides
Output Trim Range
20k
3
+V
–V
is optional and can be used to reduce error due to input
®
CC
CC
OPA628
470k
R
Trim
R
1
V
+V
IN
or Ground
CC
( R ) to –V
R
Trim
2
(1)
OPA628
R = R || R
R
3
2
CC
1
( R )
R
Trim
2
2
3
. This
12
2. The entire physical circuit should be as small as practical.
3. In general, the use of surface mount components improves
4. As with any low distortion, wide bandwidth amplifier,
5. The OPA628 should be soldered directly into the PC
of the board. A 2-ounce copper ground plane is recom-
mended. The input signal ground return, the load return,
and the power supply common should all be connected to
the same physical point to avoid ground loops which can
cause unwanted feedback.
All signal and power supply paths should be as short and
direct as possible to minimize stray capacitance and
inductance which are detrimental to high frequency per-
formance. Minimize signal trace impedance by keeping
traces as wide and short as possible. Stray capacitance
should be minimized, especially at high impedance nodes
such as the amplifier's input terminals. In addition, stray
signal coupling from the output of the amplifier back to
the input should be minimized.
performance over through-hole components by minimiz-
ing parasitics. (However, it should be noted that use of
the DIP version of the OPA628 will not compromise
amplifier performance.) If circuit elements with leads are
used, the leads should be kept as short as possible (6mm)
to minimize lead inductance. Resistors used in feedback
networks should have values of a few hundred ohms for
best performance. Shunt capacitance problems limit the
acceptable resistance range to about 1,000
end and to a value that is within the amplifier's output
drive limits on the low end. Remember that output cur-
rent must be provided by the amplifier to drive its own
feedback network as well as to drive its load.
power supply bypassing is extremely critical and must
always be used. The system power supplies should be
well bypassed at the board level with a minimum of
2.2 F tantalum capacitors. In addition, all four power
supply leads should be locally bypassed to ground as
close as possible to the amplifier pins. Surface mount
0.1 F capacitors will provide the best performance for
local bypassing. Johanson 0.1 F capacitors (part number
250R18B104ZP4W) are used on the OPA628 demonstra-
tion board. All power supply bypass capacitors should be
low impedance designs and should be located on the
primary ground plane side of the PC board for the lowest
impedance connection to ground. Properly bypassed and
modulation free power supply lines allow optimum am-
plifier performance.
board for best performance.
on the high